A stereoscopic graphics display system forms on a display screen stereoscopic images that appear to have three-dimensional qualities. Such display systems can be used advantageously in association with, for example, mechanical engineering computer-aided design systems.
A stereoscopic image of an object includes a right-eye view of the object and a left-eye view of the object. The right- and left-eye views are rendered on a two-dimensional display screen and are directed to an observer's right and left eyes, respectively. The right- and left-eye views typically differ by a preselected amount of binocular disparity that is defined by a binocular viewing model. The binocular disparity allows the observer to perceive from the right- and left-eye views the three-dimensional qualities of the stereoscopic image, which appears to lie within a three-dimensional viewing volume.
A stereoscopic graphics display system typically employs a single, fixed binocular viewing model to generate the right- and left-eye views of all stereoscopic images. The binocular viewing model is defined, for example, by a zero disparity point having a fixed location within the three-dimensional viewing volume and a disparity angle representing a fixed angle by which an image is rotated about the zero disparity point to establish the right- and left-eye views. The location of the zero disparity point is typically independent of the location of a stereoscopic image rendered within the three-dimensional viewing volume, and the magnitude of the disparity angle is typically independent of the size of the stereoscopic image.
An observer perceives the three-dimensional qualities of a stereoscopic image by "fusing" the right- and left-eye views into a single image. The fusing of the right- and left-eye views is an automatic physiological response of which most people are capable. An observer cannot fuse, however, right- and left-eye views having corresponding image components that are separated by a distance greater than a physiology-limited distance. For most observers, the physiology-limited distance is about 0.03 times the distance between the observer and the image (i.e., the viewing distance). With a viewing distance of about 60 cm., for example, a typical observer would be unable to fuse right- and left-eye views that have corresponding image components separated by a distance greater than about 1.8 cm.
In addition, most observers would be unable to fuse right- and left-eye views if the distance between corresponding image components on the display screen is comparable to the size of the image. For example, a stereoscopic graphics display system could render an image having a depth of 30 cm. and ends that each have a height of 2 cm. and a width of 2 cm. A binocular viewing model having a disparity angle of 6.degree. and a disparity point midway along the depth of the image would provide a separation of about 1.6 cm. between corresponding image components (i.e., the ends) of the right- and left-eye views. Since the separation of 1.6 cm. is comparable to the 2 cm. height and the 2 cm. width of the end of the image, a typical observer would be unable to fuse the right- and left-eye views into a single stereoscopic image.
In response to the single, fixed binocular viewing model employed in a conventional stereoscopic graphics display system, many observers manually select a relatively small disparity angle of between 2.degree. and 4.degree.. Such a small disparity angle is substantially less than the conventional default disparity angle of about 6.degree. and reduces the three-dimensional qualities of most stereoscopic images. Observers select the relatively small disparity angle, however, to avoid having to manually adjust the binocular viewing model for each different stereoscopic image. Although it avoids the requirement that the binocular viewing model be adjusted for each stereoscopic image, the use of a relatively small disparity angle reduces the three-dimensional qualities of many stereoscopic images and provides, therefore, suboptimal performance of the stereoscopic graphics display system.